This invention relates in general to a rotational driving and shaft assembly. More specifically, this invention relates to a steering shaft assembly with a slip joint having rods and linear bearings for axial movement of the steering shaft assembly.
In virtually every vehicle in use today, a steering system is provided for permitting a driver to control the direction of movement. A typical steering system includes a steering wheel, a steering shaft assembly, and a steering device. The steering wheel is rotatably supported within a driver compartment of the vehicle for movement by a driver. The steering shaft assembly is connected at one end to the steering wheel for rotation therewith. The other end of the steering shaft assembly is connected to the steering device for turning the wheels of the vehicle in response to rotation of the steering wheel. In its simplest form, the steering shaft assembly is embodied as a single shaft or tube having a pair of yokes mounted on the ends thereof. The yokes are usually connected by respective universal joints to the steering wheel and the steering device.
In many larger vehicles, such as trucks, the steering shaft assembly is designed not only to provide a rotational driving connection between the steering wheel and the steering device, but also to permit relative axial movement to occur therebetween. Such relative axial movement is advantageous for two reasons. First, a relatively small amount of such relative axial movement is desirable to accommodate vibrations, bumps, and other aspects of normal vehicle operation that would otherwise be transmitted from the steering device through the steering shaft assembly to the steering wheel. Second, when the vehicle is serviced, a relatively large amount of such relative axial movement is desirable to permit the cab of the vehicle to be pivoted upwardly without requiring disassembly of the steering system.
To accomplish this, it is known to construct the steering shaft assembly from cooperating male and female splined telescoping steering shafts. The first steering shaft is connected to the steering wheel by a first universal joint, while the second steering shaft is connected to the steering device by a second universal joint. The universal joints are provided to permit angular articulation between the steering shafts and the associated steering wheel and the steering device. The splined connection between the first and second steering shafts provides a rotatable driving connection between the steering wheel and the steering device, while permitting relative axial movement therebetween.
In the past, one or both of the splined members were coated with a material having a relatively low coefficient of friction. The low friction coating was provided to minimize the amount of force required to effect relative movement between the two splined members. Also, the low friction coating provided a relatively tight fit between the cooperating splines of the two splined members, thus minimizing any undesirable looseness therebetween while continuing to allow free axial movement.
One problem that has been experienced in connection with slip joints manufactured according to known methods is that an undesirably large gap can still exist between adjacent splines formed on the cooperating members of the slip joint even after the coating has been applied. These relatively large gaps can occur as a result of manufacturing tolerances in the formation of the individual splined members and the coating process and usually result in an undesirable amount of looseness between the splined members during operation. Looseness that occurs in the direction of rotation of the splined members, wherein one of the splined members can rotate relative to the other splined member, is referred to as backlash. Looseness that occurs in the direction transverse to the axis of rotation of the slip joint, wherein one of the splined member can extend at a cantilevered angle relative to the other splined member, is referred to as broken back. Known solutions to the problems of backlash and broken back have been found to be relatively difficult, costly, and time consuming to employ. Thus, it would be desirable to provide an improved slip joint that results in precise conformance between the slip joint members, thus, minimizing the adverse effects of backlash and broken back.